The present invention relates to a method for cleaning tanks, such as storage tanks and ship tanks.
1. Field of the Invention
Hitherto such tanks were vented, in particular after having contained hazardous materials such as benzene. Venting is a time-consuming blower operation, accompanied by development of vapours, which may be hazardous to the environment. Therefore the exciting vapours have to be burned in an incinerator, or alternatively ships have to vent in the open sea. Thus both alternatives are expensive.
2. Description of Related Art
GB-A-470,419 relates to a method and apparatus for cleaning the interior of enclosed spaces such as tank cars, fuel tanks and oil and chemical carrying containers which may have become fouled on their interior surfaces. The method comprises introducing a solvent into the enclosed space in both vapour and liquid form, and removing the liquid solvent containing dissolved impurities from the enclosed space.
U.S. Pat. No. 3,046,163 relates to a method and apparatus for interiorly cleaning a tank by first passing a hot vapour of a chlorinated hydrocarbon solvent into the tank, condensing said vapour on the tank walls, draining off the contaminated condensate and recovering the solvent, followed by pressure spraying the interior with liquid solvent, then again passing hot solvent vapour into the tank and finally passing unheated outside air through the tank to remove remaining traces of solvent vapour from the air.
The above patents both relate to a method for removal of residual material clinging to the walls of a tank, using a suitable solvent and recirculating the recovered solvent until said material has been removed from the walls and apparatus suitable for use in said method.
As both patents expired well over twenty years ago it would have been obvious to use these methods and apparatus as an easy way out to avoid the high costs and environmental damage of the venting system as presently used, but apparently these methods and apparatus were not sufficiently refined to obtain adequate cleaning of tanks.
The above disadvantages are avoided by the method according to present invention.